One example of a wireless communication system is a Multi-channel Multi-point Distribution System (“MMDS”), which offers broadband data and voice transmission over a terrestrial microwave platform. MMDS can deliver, for example, multi-channel television programming, Internet access and content, voice communications, data transfer services, and other interactive services. MMDS typically operates in the 2.5 GHz band in North America and in the 3.5 GHz band in international markets. Also, the United States Federal Communications Commission (“FCC”) has allocated the 27.5 to 29.5 GHz band to Local Multi-point Distribution Services (“LMDS”). Signals typically are transmitted within a line of sight (“LOS”) from a base station transmit antenna to a subscriber's receive antenna (“downstream” transmission), and from a subscriber's transmit antenna to a base station's receive antenna (“upstream” transmission).
Wireless communication systems, such as, for example, MMDS, are well suited to serve the small office/home office (“SOHO”), telecommuter, and small business market, although they may be used in other markets, such as residential, medium business and large business. Wireless communication systems also are well suited to provide communication services to remote and difficult to reach locations.
At present, broadband wireless communication systems, including those in the MMDS band, depend upon antenna height to allow reasonable coverage of large areas with a small number of base stations. Base station antennas may be placed, for example, on mountain tops, tall buildings, or towers such as, for example, existing cellular towers.
Presently, base station antennas typically use omni-directional, cardioid antenna patterns for downstream transmission and azimuthally-sectored antenna patterns for upstream transmission reception. The increased gain of the sectorized upstream antenna pattern helps to balance the signal-to-noise ratio (“SNR”) margins between the upstream and downstream cases due, at least in part, to differences between the transmit power of the base station and the transmit power of the subscriber.
The capacity of each base station is limited by a number of factors. For example, the downstream capacity may be limited by the absence of frequency re-use. The upstream capacity may be limited, for example, by available RF bandwidth, spectrally inefficient modulation, and low transmit power at the subscriber transmitter. At present, each base station is limited to approximately 10,000 subscribers.
Current wireless communication systems, including MMDS systems, require complex installation procedures due to the need for a clear LOS from the subscriber location to the base station antenna. Service providers must perform time consuming pre-installation site surveys to assure that the LOS condition is met. However, it is frequently not possible to provide a clear LOS to every subscriber. For example, in the San Francisco Bay area, only approximately 40% of the requested installations can be performed. The installations which proceed are very costly because they require carefully positioned and pointed antennas at both the base station and the subscriber location. Typically, the antenna at the subscriber location must be positioned outdoors, typically high up on a roof or tower, and associated grounding and wiring must be run inside.
Like reference symbols in the various drawings indicate like elements.